Pyrometer for measuring the temperature of a gas component within a furnance

ABSTRACT

A pyrometer for use in measuring temperatures in a furnace, has a lens-tube for supporting an optical head in a port of the furnace for viewing an interior of the furnace along a line of sight. The optical head converts infrared radiation to electrical signals. A photometer circuit connected to the optical head processes the electrical signals and a scaling circuit connected to the photometer circuit scales the electrical signals. An output circuit connected to the scaling circuit receives the scaled electrical signals and produces output signals for display or control of the furnace. A power supply connected to the scaling circuit powers the photometer, scaling and output circuits. Calibration in the scaling circuit scales the electrical signals to be most sensitive to a wavelength of middle infrared radiation to which at least one gas component in the furnace is semi-transparent, for measuring the temperature of the at least one gas component.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates in general to temperature sensors,and in particular, to a new and useful optical pyrometer for measuringfurnace gas temperatures.

[0003] 2. Description of the Related Art

[0004] Prior devices have measured the temperature of entrained fly ashto determine gas temperature, limiting their application to only fuelswith a high ash content. The present invention measures the temperatureof actual constituent gases, thereby providing accurate temperaturemeasurement with any fuel.

[0005] Radiation pyrometry, more commonly called optical pyrometry,measures the temperature of a substance by measuring the thermalradiation emitted by the substance.

[0006] Thermal radiation is a universal property of matter that ispresent at any temperature above absolute zero. Optical pyrometryutilizes the fact that the thermal radiation emitted by most substancesis continuous over a spectral range of approximately 0.3 micron to 20microns. This spectral range encompasses ultraviolet (UV) radiation, upto 0.38 micron; the visible (VIS) range, 0.38 to 0.78 micron; andinfrared radiation (IR), 0.78 to 20.0 micron. IR radiation is furtherdivided into three segments, near IR (0.78 to 3.0 micron), middle IR(3.0 to 6.0 microns), and far IR (above 6 microns).

[0007] The distribution of the thermal radiation of a substance over thespectral range is a function of both the temperature and emissivity ofthe substance. Higher temperatures shift the distribution toward theshorter wavelengths; lower temperatures shift the distribution towardthe longer wavelengths. Higher emissivity increases the thermalradiation at any given temperature, whereas lower emissivity reduces thethermal radiation at the same temperature. A perfect thermal radiator iscalled a black-body, and has an emissivity of 1.0. Thermal radiatorsthat are not perfect and that emit thermal radiation in the samespectral distribution as a black-body, but at reduced intensity, arecalled gray-bodies and have emissivities from zero to 1.0.

[0008] Emissivity can vary equally over the spectral range, called totalemissivity; or it can vary as a function of the wavelength over thespectral range, called spectral emissivity. Both total emissivity andspectral emissivity can also vary as a function of the temperature ofthe substance. All of these emissivity variations can occurindependently and simultaneously.

[0009] Scattering and absorption are two other important phenomena thataffect intensity and distribution of the thermal radiation propagatingthrough a medium, as well as the transmission distance (effective depth)through the medium. Scattering diffuses the thermal radiation, is highlydependent on both the species and physical size of the constituents ofthe medium, and increases significantly as the wavelength decreases.Absorption of thermal radiation is generally wavelength specific; theabsorbed wavelength(s) being dependent upon the species that are exposedto the thermal radiation.

[0010] Optical pyrometry utilizes all of these radiating and propagatingproperties of matter to ascertain the temperature of a substance througha medium by measuring the intensity of the thermally radiated UV, VIS orIR energy of the substance. The radiating properties of matter aredefined by Planck's equation for spectral emissivity and theStefan-Boltzmann law for total radiated energy. The propagatingproperties through a medium are defined by the Boujuar-Lambert law forabsorption and the Rayleigh and Mie equations for scattering.

[0011] Optical pyrometers can be either narrow bandpass or broadbandpass instruments. Typically, narrow bandpass optical pyrometersutilize Planck's equation to determine temperature, whereas broadbandpass optical pyrometers use the Stefan-Boltzmann law. Opticalpyrometers are also classified according to the particular wavelength(s)utilized in determining the measured temperature, i.e., UV, VIS, or IR.Usually, the shorter wavelengths (UV, VIS and near IR) are used forhigher temperature measurements, whereas longer wavelengths (middle andfar IR) are used for lower temperature measurements.

[0012] Successful implementation of any optical pyrometer requires anextensive analysis of the application to determine the properwavelength, bandpass and emissivity based on the characteristics of themeasured substance over the desired measurement temperature range.Additionally, scattering and absorption in the propagating medium mustalso be considered to ensure that the measured thermal radiation isactually proportional to the measured temperature, and also to ensurethe correct measurement depth into the propagating medium. This isespecially important for boiler/furnace applications because themeasured substance according to the present invention, flue-gas, isquite nebulous and its constituents can vary widely over normaloperating conditions.

[0013] Without conducting the proper application specific analysis, mostoptical pyrometers cannot reliably and accurately measure boiler/furnacefireside gas temperatures. Typical VIS and broad bandpass IR typedevices have a very short effective depth, and only measure thenear-field temperature. Typical narrow bandpass IR type devices have anextremely long effective depth, and are greatly influenced by theopposite wall surface temperature.

[0014] U.S. Pat. Nos. 5,112,215 and 5,275,553, which are bothincorporated here by reference, disclose optical pyrometers formeasuring temperature based on single and double wavelength measurementsof radiation from fly ash in a furnace.

SUMMARY OF THE INVENTION

[0015] The invention is an optical pyrometer which is based on Planck'sequation and which utilizes specific wavelengths to measure the actualtemperature of constituent gases in the furnace and the convection passsection of a boiler. Specifically, the invention uses 1.38 microninfrared radiation to measure the temperature of H₂O in a constituentgas that is a product of combustion of any hydrocarbon or carbon fuel.Alternative ranges of wavelengths are 1.8 to 2.0 micron and 2.3 to 3.1micron, providing temperature measurement of H₂O, CO₂, or mixtures ofH₂O and CO₂.

[0016] The invention is primarily intended for applications onpulverized coal fired boilers, with boiler widths of 40 to 100 feet, andfor all types and classes of coals. The standard calibration for theinvention is made for measuring fireside gas temperatures from thefurnace exit through the convection pass. With proper wall penetrationhardware, the invention can be used on all normal forced draft, balanceddraft, and induced draft boilers.

[0017] The invention can be used as a field diagnostic tool as well as apermanently installed on-line monitor. As a diagnostic tool, it can beused as a stand alone instrument, or along with data acquisitionequipment to record data for extended tests. As a permanently installedon-line monitor, it can also stand alone or serve as an integral part ofa larger system to implement automatic monitoring and control.

[0018] The invention, being an optical pyrometer, will measuretemperature based on the light intensities that it sees. However, it isspecifically tuned and calibrated to measure fireside gas temperature.Hence, it will not provide an accurate temperature reading of solidobjects nor any other medium than fireside gas streams.

[0019] The invention measures the average temperature of a gas in asolid cone of about 6 degrees, along the line-of-sight of its lens-tubeaxis, over the entire length of the line-of-sight. The actualmeasurement contribution from any point within the cone of view varieswith the fourth power of the temperature of the point; and also as adecreasing exponential into the gas stream depth. Hence, the averagetemperature indicated by the invention will be weighted toward thehighest temperature in the field of view, and also slightly more towardthe near-field rather than the far-field. The actual depth ofmeasurement is also a function of optical scattering, consequently itwill vary slightly with gas-stream particle load, gross unit, load, andexcess air.

[0020] The invention requires an unobstructed field of view of themeasurement area, especially in the near field. The 6 degree conicalfield-of-view equates approximately to a diameter of 5 feet at adistance of 50 feet. However, since the measurement contribution fromany point decreases exponentially with distance, partial obstructionssuch as pendants and wing walls beyond a distance of 50 feet have verylittle effect on accuracy.

[0021] The accuracy of the invention is about +/−50 F for normalpulverized coal fired utility boilers with furnace widths of 40 to 100feet. Furnace widths of less than 40 feet may require specialcalibration to provide the specified accuracy. Furnace widths greaterthan 100 feet may require multiple units to provide full widthtemperature coverage.

[0022] Since the invention is tuned for specific gas species in thefireside gas stream, the opposite walls have very little influence onits measurement accuracy. Also, since the opposite walls are farthestfrom its objective lens, their effect is minimized by the exponentialdecrease of response with distance.

[0023] The usual measuring temperature range for the invention is 1000 Fto 2800 F. (approximate). Special calibration for other temperatureranges can be provided to lower the range to 700 F minimum or increasethe range to 3000 F maximum, without degradation of measurementaccuracy.

[0024] The invention is designed for installation at any location fromthe furnace exit, throughout the convection pass section. It can beinstalled at any standard furnace observation port, or any other wallpenetration, i.e., sootblower or thermoprobe location, etc. A suitablewall box should be installed in the boiler wall for permanentinstallations.

[0025] For accurate measurement, the invention should be installed at alocation with a 40 to 100 foot line-of-sight. For most boilers this isacross the boiler width rather than from front wall to rear wall.Special care should be taken to avoid nearness to corners, pendants andwing walls that can restrict the 6 degree conical field-of-view in thenear field. The optical head includes a lens for focusing infraredradiation from a line-of-sight cone of a solid angle of about 3 to 8degrees from the furnace.

[0026] The invention is not intended to measure actual combustiontemperature. Generally, the 1000 F to 2800 F measurement range willinherently prevent installation too close to the furnace combustionzone. However, for some applications, combustion temperatures can beless than 2800 F., and care should be exercised to ensure that themeasurement zone is well clear of the combustion zone.

[0027] Since the average temperature indicated by the invention isweighted toward the highest temperature in the field of view, and alsotoward the near-field rather than the far-field, multiple units can beutilized to indicate temperature variation across the furnace width. Forbest results, the furnace width should be 50 feet or greater, and theunits should be installed in pairs; one on each sidewall, on oppositeends of the same line-of-sight.

[0028] An object of the present invention is to provide a furnacepyrometer which is specially designed to achieve the foregoing functionsin an effective manner.

[0029] A further object of the present invention is to provide a furnacepyrometer which is specially designed to sense the intensity ofintermediate infrared radiation which is characteristic of one or morespecific gas constituents generated by the combustion of hydrocarbon orcarbon fuel including coal, natural gas, oil, organic matter or othercombustible fuel.

[0030] A still further object of the present invention is to provide apyrometer which is simple in design, rugged in construction, andeconomical to manufacture.

[0031] The various features of novelty which characterize the inventionare pointed out with particularity in the claims annexed to and forminga part of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich the preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the drawings:

[0033]FIG. 1 is a schematic representation showing the placement of thepresent invention and its field of view compared to prior artpyrometers;

[0034]FIG. 2 is a graph plotting the uncertainty in temperature againstcoal composition for different blends, comparing the error in knownpyrometers to the error of the present invention;

[0035]FIG. 3 is a horizontal sectional view of the enclosure portion ofthe pyrometer according to the present invention;

[0036]FIG. 4 is a vertical sectional view of the pyrometer of thepresent invention;

[0037]FIG. 5 is an enlarged vertical sectional view taken from area 5 ofFIG. 4;

[0038]FIG. 6 is a side elevational view of the present invention mountedin the wall of a furnace and with representative dimensions shown in thefigure;

[0039]FIG. 7 is a rear elevational view of the pyrometer of the presentinvention; and

[0040]FIG. 8 is a view of the circuit components of the presentinvention removed from their enclosures.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041] The pyrometer of the present invention, generally designated 10in FIG. 1, is smaller, more cost effective and directly measures theactual furnace gas temperature rather than the entrained fly ashtemperature, which was the case for prior art pyrometers shown at 11 and13 in FIG. 1. Also as shown in FIG. 1, the direct measurement of furnaceand convection pass gas temperatures is effective deeper into thefurnace than with regard to fly ash measurements obtainable by prior artpyrometer 11. Additionally, the depth of measurement of the presentinvention is shallower than that of prior art pyrometer 13 and lieswithin the confines of the furnace, thus avoiding undesirable walleffects on temperature measurements associated with prior art pyrometer13. Direct gas temperature measurement with the present invention alsoprovides direct evidence of boiler cleaning effectiveness. Inadequatecleaning causes furnace slagging, convection pass fouling and increasedNOx emissions. The pyrometer of the present invention measures gastemperature by simply aiming its lens through any available inspectionport in a boiler.

[0042] The advantages of measuring gas temperature rather than fly ashtemperature are evident in FIG. 2 which compares errors in temperaturemeasurement to coal mixtures from 100% Eastern coal which in the priorart pyrometer gave an error from about 50 to about 250 F above actual,to 100% Western coal which gave an error of about −50 to −250 F This iscompared to the uncertainty of the present invention which variesbetween about +/−50 F for the same coal compositions.

[0043] Also shown in FIG. 1, the present invention, by being constructedand calibrated for specific IR wavelengths of gases which are known tobe present, has a depth of measurement of from about 40 to about 100feet into the furnace.

[0044] The selection of wavelengths for which the present invention isparticularly sensitive is an important aspect of the invention.

[0045] A wavelength for which the gas is transparent would result in ameasurement of the temperature of the opposing wall. On the other hand,a wavelength for which the gas is opaque would result in a measurementof the gas temperature at the near wall. What is desired is a wavelengthfor which the gas is semi-transparent.

[0046] Mathematically, the transmission T through the hot gas can bewritten as

T(y)=e ^(−k(y)(H2O)X)

[0047] where

[0048] k(y) is the spectral absorption coefficient

[0049] [H₂O] is the concentration of H₂O

[0050] X is the path length.

[0051] The desired wavelength will be one for which T is essentiallyzero for values of X≧the distance to the far wall and for which T isnearly 1 for values of X≦2 feet. FIGS. 3-8 illustrate the constructionof the present invention.

[0052] The invention utilizes a THROUGH-THE-LENS-PYROMETER (TLP) circuit12 (FIG. 4) of the type used with known IR cameras, and utilizes much ofthe compact, rugged hardware of the CARRY-OVER-MONITOR-SYSTEM (CMS). ACMS lens-tube 14 provides mounting for the detector (photometer) circuit12, objective lens 16 (FIG. 5), and IR bandpass filter 18. A CMSair-shroud, made up of inner and outer concentric tubes 22, 24, providesa means to cool the internal lens-tube components and aspirate theobjective lens 16.

[0053] The shroud formed by outer tube 24 ends at a cap 26 having anaperture 28. Cooling gas is supplied by a fitting 29 shown in FIG. 3,and the cooling gas flows between the inner and outer tubes, 22, 24 tothe interior of cap 26 wherein it is directed to purge the lens-tubecomponents as it leaves the cap 26.

[0054] As shown in FIG. 5, the optical head generally designated 30 ofthe pyrometer also includes a sapphire window 32, a lens retainer 34, alens housing 36, a gasket 38, an O-ring 39, a filter holder 40 and anoptical detector 42 in the form of a germanium photodiode.

[0055] The lens-tube 14 and air-shroud are mounted on the front of asmall watertight electronics enclosure 44 that houses additionalcircuitry that provides temperature scaling and DC power. This enclosurealso houses a digital display 46 and analog output connector 48, bothmounted on the rear panel 43. Incoming 120/240 VAC, 50/60 HZ power isvia water tight cable 50 through the enclosure rear panel. Rear panel 43also carries an analog thermometer 45 for monitoring the enclosuretemperature which must be below 130 F.

[0056] The circuitry for the invention is divided into three basicsections, and is mounted on three separate circuit boards: thephotometer circuit on circuit board 12; a scaling circuit on circuitboard 52; and the power supply circuit on circuit board 54.

[0057] The photometer circuit 12, an adaptation of the TLP detectorcircuit, consists of the germanium photodiode 42 and conventionaltransimpedance amplifier circuit. An offset adjustment is provided forzero calibration, and an adjustable gain stage is provided for fullscale calibration, all on circuit board 12. A 125 second integratoreliminates measurement flicker, and an emissivity adjustment stageallows for application specific calibration, i.e. field calibration, ifnecessary for special applications. Circuit 12 is connected to thecircuit in the board 52 by a cable 55 as best seen in FIG. 8.

[0058] The scaling circuit board 52 consists of both the scaling circuitand an analog output circuit.

[0059] The scaling circuit converts the photometer circuit's output toan equivalent temperature signal for the digital display 46 and analogoutput circuit. These signals are sent along a cable 56. The scalingcircuit also has an internal autocalibration feature that eliminates theneed for fine tuning adjustments and compensates for ambient temperaturedrift during operation. Autocalibration is invoked every 76 secondsduring operation.

[0060] The analog output circuit which is also on circuit board 52,consists of an isolated voltage-to-current (V/I) converter that providesthe 4 to 20 milliamp analog output signal and the 1500 volt isolation.The V/I converter output is provided with an internal, isolated, 24 VDCpower supply for self-powered, stand-alone operation; or it can bedirectly connected in any loop powered system. Separate pins areprovided in the output connector for each option. Both output optionsare protected by a common surge suppressor and fuse.

[0061] The power supply circuit 54 provides the necessary powerconversion and isolation for all of the other circuitry and is connectedto board 52 by a cable 57. An internal fuse provides short circuitprotection and an internal power line filter suppresses incoming andoutgoing conducted Electromagnetic-Interference (EMI). Jumpers on thepower supply circuit board provide selection of 120 or 240 VAC 50/60 HZincoming power. These are plug-onjumpers, initially configured for 120VAC 50/60 HZ, but can be easily reconfigured for 240 VAC 50/60 HZoperation.

[0062] The digital display 46 is a 0 to 2 VDC (1.9999 volt), 4½ digitLCD panel meter with back lighting. Only 4 of the digits are used andthe decimal point is disabled.

[0063] Cooling in enclosure 44 is by compressed air supplied to a vortexcooler 60 with a block 62 for supply of cool air at 64 and exit at 66.Air supply is at 68.

[0064] As best shown in FIG. 6, the pyrometer 10 of the presentinvention can be inserted and retracted along a rod 70 and held in placeby a set screw 72. Tube 14 has a heat shield 74 mounted thereon so as tohave portion of tube 14 beyond the heat shield 74 extending through amounting flange 76 having a seal plate 78. The tube extends into a pipesleeve 80 which encloses the portion of the tube containing cap 26,sleeve 80 extending into a wall port 82 in the furnace wall 84. Heattransfer tubes in the wall are represented by a tube 86 with the port 82being provided between two adjacent tubes.

[0065] Referring to FIG. 8, the photometer circuit with the germaniumphotodiode has a conventional transimpedance amplifier circuit 90 thatdetermines dynamic measurement range, an adjustable gain stage for fullscale calibration at opamp 94, an offset adjustment stage for minimumscale calibration at opamp 92, an integrator with a total settling of125 seconds to overcome measurement flicker at opamp 96 and anemissivity adjustment stage for field calibration also at opamp 96.

[0066] The gain 98 and offset 100 adjustments provide a means tocalibrate photometer circuit response to a black-body calibration(temperature) source.

[0067] The emissivity adjustment provides a means for applicationspecific field adjustment, if necessary, and is physically located at115 on the scaling/output circuit board.

[0068] Additional support circuitry on this board consists of athermistor (RT) controlled photodiode heater (HTR) with adjustabletemperature setting opamps and an analog switch 99 that provides acalibration reference voltage for field adjustment of emissivity.

[0069] A fixed resistor may be substituted for an adjustable temperaturesetting potentiometer 101 for the photodiode heater.

[0070] The scaling circuit 52 consists of an Analog/Digital Converter(ADC) 107, a Programmable Read Only Memory (PROM) 104, a Digital/Analogconverter (DAC) 102 and clock/timing support circuitry. The ADCdigitizes the 0 to 10 volt intensity signal from the photometer boardinto a unique PROM address. Each PROM address location contains acorresponding predetermined digital temperature value for each digitizedintensity. The DAC then converts the digital temperature value at thePROM address back into a 0 to 5 volt analog signal representative oftemperature.

[0071] The particular ADC selected for the scaling circuit (AD677) hasan internal autocalibration feature that eliminates the need for finetuning adjustments and also compensates for ambient temperature driftduring operation. Since the incremental resolution of the incomingsignal to the ADC is approximately 150 microvolts per bit (correspondingto approximately 10 F change at low end of scale), this feature isnecessary to eliminate excessive measurement drift at the low end of themeasurement range. Autocalibration is invoked every 76 seconds duringoperation.

[0072] It should be noted that the ADC output code is the bipolar twoscomplement of the input signal. In order to accommodate this dataformat, the 0 to 10 VDC intensity signal from the photometer board isconverted to −5 to +5 VDC bipolar input signal by opamp 109 and voltagereference 122. Also, since the ADC output is 16 bit serial format, two 8bit shift registers 108 are used to convert the ADC output to parallelformat for the PROM. The twos compliment output code from the shiftregisters is then converted to offset binary code for the PROM addressby inverting the most significant bit with a NAND-gate.

[0073] The 8 bit parallel digital output data from the PROM is convertedto a 0 to 2 milliamp output signal by the DAC. The DAC output signal isthen converted to a 0 to 5 VDC signal by opamp 106.

[0074] The clock/timing circuitry provides all of the essential signalsto initiate the ADC conversion, read data from the PROM, write data tothe DAC and autocalibrate the ADC. The basic clock circuit is an R/Crelaxation oscillator utilizing NAND-gate 110 to provide the approximate900 KHZ CLK signal to the ADC and also to the additional timing circuitsfor ADC data sampling (SAMP), PROM output enable (OE) and DAC write(WR), ADC autocalibrate (CAL), and DAC disable (CE) duringautocalibrate. These additional timing functions are derived from theCLK signal by binary counter dividers 112, 114 and one-shotmultivibrator pulse shapers 111, 113.

[0075] The SAMP pulse is a 10.6 microsec pulse at a 144 microsec period(approximately 7 KSPS sample rate), generated by dividing the CLK signalby 128 with binary counter 114 and one-shot multivibrator 113. The ADCsamples the input signal (VIN) on each occurrence of the falling edge ofthe SAMP pulse. This sample rate is approximately seven times theminimum sample rate for the ADC, thus ensuring that excessive ADC droopdoes not occur between samples. During the SAMP pulse the CLK signal tothe ADC is gated off by NAND-gate 110 to prevent digital feedthroughnoise from the CLK input to the ADC. The ADC requires approximately 19microsecs to complete a conversion.

[0076] The UPDATE signal is a 1.2 microsec pulse at an 18.4 millisecperiod (approximately 54 times per second), generated by dividing theCLK signal by approximately 16,000 with binary counter 114 and one-shotmultivibrator 113. This pulse is negative true, and triggers the PROM toread the address from the ADC on the leading (falling) edge; the PROM'soutput data is valid approximately 200 nanosecs later. The trailing(rising) edge of this same pulse triggers the DAC to latch the outputdata from the PROM. The DAC output is then updated to new dataapproximately 100 nanosecs later. This results in updating the analogoutput and digital display approximately 54 times per second. Anintegrator at opamp 109, with a total settling time of approximately 3seconds, smooths the DAC output signal to analog output and display.

[0077] The ADC CAL signal is a 10.2 microsec pulse at approximately 76second intervals, generated by dividing the CLK signal by 67,000,000with binary counters 114 and 112 and one-shot multivibrator 111.Autocalibration of the ADC requires approximately 96 millisecs. At thestart of autocalibration the CALDIS signal, a 127 millisec pulsegenerated by one-shot multivibrator U14B, disables the SAMP and UPDATEpulses and the DAC chip enable (CE) thus preventing erroneous data fromoccurring during and immediately following calibration.

[0078] An isolated voltage-to-current (V/I) converter 116, with 1500volt isolation capability, converts the 0 to 5 VDC signal from the DACand opamp 106 to the 4 to 20 milliamp analog output signal. The V/Iconverter output is provided with an isolated 24 VDC power supply forself-powered, stand-alone operation; or it can be directly connected ina loop powered system. Separate pins are provided in the analog outputconnector for each option. Both output options are protected by a commonsurge suppressor (MOV1) and fuse 222.

[0079] The power supply circuit 54 consists of three separate powersupplies: the +5 VDC LOGIC supply, the +/−15 VDC and +/−12 VDC ANALOGsupply, and the +24 VDC ANALOG OUTPUT supply. The LOGIC supply and theANALOG supply share a common stepdown transformer 200 and signal ground(COM). The ANALOG OUTPUT supply has a separate stepdown transformer 202and is isolated from the LOGIC and ANALOG signal ground to provideproper isolation for the analog output V/I converter.

[0080] A common 2 amp, 250 volt fuse 203 provides short circuitprotection for both transformers. Both transformers' primaries areconnected to a common jumper circuit that provides selection of 120 or240 VAC 50/60 incoming power. These jumpers are initially configured for120 VAC 50/60 HZ, and moving the jumpers enables supply of 240 VAC 50/60HZ power. A common incoming line filter 204 is provided at the incomingpower connections (transformers' primaries) to suppress incoming andoutgoing conducted EMI.

[0081] The LOGIC and ANALOG supplies are powered by a dual winding 20 VAstepdown transformer (14A-20-515), specifically designed for +5 VDC and+/−15 VDC power supplies. Conventional bridge rectifiers 205 and filtercapacitors also at 205 provide unregulated DC to each voltage regulator206. The voltage regulators provide the necessary line/load regulationto maintain the output voltages within the +/−5% requirement.

[0082] In addition to the +/−15 VDC ANALOG supply for the bulk of theanalog circuitry, the ADC requires +/−12 VDC. This supply is derivedfrom the +/−15 VDC via series zener diodes. These zeners are biased withadditional load resistors to provide +/−12.08 VDC with the 12 mA load ofthe ADC.

[0083] The +24 VDC ANALOG OUTPUT supply is powered by a separate 2.5 VAtransformer (14A-2.5-20). This transformer has two 10 VAC secondarywindings connected in series to provide 20 VAC. A conventional bridgerectifier and filter capacitor provides 28 volt unregulated filtered DC.Since normal +/−10% line voltage variations could cause this powersupply output to exceed the 30 VDC max rating of the V/I converter, aseries zener diode and additional bias resistor is used to drop theoutput to 28.22 VDC max.

[0084] The digital display 46 is a 0 to 2 VDC (1.9999 volt), 4½ digitSimpson type M145 LCD panel meter with back lighting. Only 4 of thedigits are used and the decimal point is disabled. A precision voltagedivider, located on the scaling/output circuit board, rescales the 0 to5 VDC output signal from opamp 106 to the 0.1 millivolt per degree F.required for direct display of temperature in degrees F.

[0085] While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A pyrometer for use in measuring temperatures ina furnace, comprising: support means for supporting an optical head in aport of the furnace for viewing an interior of the furnace along aline-of-sight, the optical head converting infrared radiation intoelectrical signals; a photometer circuit connected to the optical headfor processing the electrical signals; a scaling circuit connected tothe photometer circuit for scaling the electrical signals; an outputcircuit connected to the scaling circuit for receiving scaled electricalsignals and producing output signals; output means connected to theoutput circuit for use to display the output signals or to supplyinformation corresponding to the output signals or to use the outputsignals as control signals for the furnace; power supply connected tothe scaling circuit for powering the photometer, the scaling and theoutput circuits; and calibration means in the scaling circuit forcalibrating the scaling of the electrical signals to be most sensitiveto a wavelength of middle infrared radiation to which at least one gascomponent in the furnace is semi-transparent, for measuring thetemperature of the at least one gas component.
 2. A pyrometer accordingto claim 1, wherein the support means comprises a lens-tube having oneend extending into the port of the furnace and an opposite end, anenclosure connected to the opposite end of the lens-tube, and at leastone circuit board in the enclosure for supporting the scaling circuit,the output circuit and the power supply.
 3. A pyrometer according toclaim 2, including a circuit board in the lens-tube for supporting thephotometer circuit.
 4. A pyrometer according to claim 3 including a heatshield around the lens-tube and at an entry location the lens-tube intothe furnace port.
 5. A pyrometer according to claim 1 including gascooling means connected to the support means for cooling the opticalhead.
 6. A pyrometer according to claim 2 including gas cooling meansconnected to the enclosure for cooling the enclosure.
 7. A pyrometeraccording to claim 6 wherein the lens-tube comprises inner and outertubes with a gas space therebetween, the cooling means including meansfor supplying cooling gas to the space between the inner and outer tubesfor cooling the optical head.
 8. A pyrometer according to claim 7including a cap with an aperture connected to the end of the lens-tubein the furnace port for directing the cooling gas as it leaves thelens-tube to purge the lens-tube.
 9. A pyrometer according to claim 1wherein the means for calibrating the scaling circuit comprise means forscaling the electrical signals to be most sensitive to infraredradiation between about 1.3 and 3.1 microns.
 10. A pyrometer accordingto claim 9 wherein the means for calibrating the scaling circuit scalesthe electrical signals to be most sensitive to infrared radiation atabout 1.38 microns for measuring the temperature of H₂O.
 11. A pyrometeraccording to claim 9 wherein the calibration means scales the electricalsignals to be most sensitive to wavelengths between 1.8 and 2.0 microns.12. A pyrometer according to claim 9 wherein the calibration meansscales the electrical signals to be most sensitive to wavelengthsbetween 3.3 and 3.1 microns.
 13. A pyrometer according to claim 1wherein the optical head includes a lens for focusing infrared radiationfrom the furnace, an IR bandpass filter for passing the focused infraredradiation between about 1.3 and 3.1 microns wavelength, and aphotodetector for receiving the focused and filtered radiation.
 14. Apyrometer according to claim 13 wherein the photodetector comprises agermanium photodiode.
 15. A pyrometer according to claim 1 wherein theoptical head includes a lens for focusing infrared radiation from aline-of-sight cone of a solid angle of about 3 to 8 degrees from thefurnace, an IR bandpass filter for passing the focused infraredradiation, and a photodetector for receiving the focused and filteredradiation.
 16. A method of measuring temperature in a furnacecomprising: positioning a pyrometer having an optical head in a port ofthe furnace, with a line of sight intersecting a passage of gas in thefurnace containing a plurality of gas components; receiving infraredradiation from the gas as it passes the line of sight; converting theinfrared radiation in the optical head to electrical signals; andscaling the optical signals to maximize signals generated by infraredradiation which is semi-transparent to the gas components.
 17. A methodaccording to claim 16 including scaling the electrical signals forinfrared radiation in a wavelength range of about 1.3 to about 3.1microns.
 18. A method according to claim 17 including scaling thesignals for infrared wavelengths of about 1.38 microns for sensing thetemperature of H₂O as the gas component trade.
 19. A method according toclaim 16 including scaling the electrical signals for wavelengthsbetween 1.8 and 3.1 for measuring the temperature of mixtures of H₂O,CO₂ or mixtures thereof.